The Tetra Tech Geomatics Technology Team was contracted by Rooney Engineering, a Tetra Tech company, in 2013 to provide orthoimagery for a 50-mile segment of corridor for a pipeline-planning project across Southern Pennsylvania and Northern Ohio.

The initial 50-mile segment included a 2,000’ wide corridor that was covered by 834 images acquired with an UltraCamX digital camera. 38 targeted ground control points were surveyed. Tetra Tech delivered 290 image tiles of 2,000’ by 2,000’ with 3” ground sample distance in geotiff and MrSID formats.

Between 2013 and 2015, three follow-up projects covered segments along the planned pipeline from Southeastern Pennsylvania into Northern Ohio. The follow-up projects consisted of a 250-mile segment and about 20 smaller segments, covering alternate routes mapping the construction progress. Imagery was acquired with various UltraCam models X, Falcon and Eagle. A total of almost 7,000 images were collected for the 4 projects. For some of the blocks in the follow up projects no additional ground control was surveyed. Instead, so called ‘2nd generation orthoimagery’ was created. The new imagery was tied into the existing imagery during aerotriangulation. For that purpose the flight layout for the new blocks was designed so that it overlapped with previous flights.

LiDAR data and LiDAR derived terrain elevation data were downloaded from Pennsylvania’s PAMAP website to provide terrain support for the orthoimagery. In areas were terrain change had occurred due to new construction of highways, railroads, parking areas, overpasses or new subdivisions automatic terrain extraction with subsequent manual editing was used to create a new terrain model. The orthoimagery was delivered in 2,000’ by 2,000’ tiles. Tile names were derived from the SW corner coordinates, preceded by a string to avoid duplicate file names should a tile be covered in multiple epochs of imagery.

The positional RMSE of the orthoimagery was well within the required half footor 2 pixel requirement and the RMSE of the ‘2nd generation orthoimagery’ was well within 1’ or 4 pixel RMSE.